Solids conveying with multi-diameter piping circuit

ABSTRACT

A mixture of gas and solid particles are conveyed through a piping circuit connected between initial and terminal points. The gas is introduced at the initial point and the particles are introduced between the initial and terminal points. A diameter of the piping circuit increases downstream of where the particles are introduced, and a velocity of the gas is at least as great as a pick-up velocity of the particles at the point where the particles are introduced into the piping circuit. In addition to the above constraints, the piping circuit is sized so that total pressure losses due to flow in the piping circuit between the initial and terminal points are within a designated amount.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation in part of and claims priority to andthe benefit of co-pending U.S. patent application Ser. No. 16/904,334,filed Jun. 17, 2020, which claimed priority from U.S. ProvisionalApplication Ser. No. 62/863,040, filed Jun. 18, 2019, the fulldisclosure of which are incorporated by reference herein in theirentireties and for all purposes.

BACKGROUND OF THE INVENTION 1. Field of Invention

The present disclosure relates to a system and method for conveying amixture of particles dispersed in a gas.

2. Description of Prior Art

Particulate material is sometimes conveyed through piping, and isdispersed in a pneumatic stream or another vapor. These types ofconveying systems are usually referred to as either a dilute phasesystem or a dense phase system. Dilute phase conveying systems oftenmeter particulate material into the piping from a hopper or otherretainer. A standard blower, compressor, or pressure from a processdelivers a high volume of air (or inert gas) at a low pressure,typically not exceeding 15 psig, which is used to convey a low volume ofparticulate material. The stream travels at high velocities to keep theparticulates suspended in the flowing medium. In dilute phase conveyingsystems, the particulate material being conveyed is usually very freeflowing, and the solids loadings is relatively low, typically on theorder of 5 to 15 pounds of particulate material per pound of gas. Dilutephase systems usually convey non-abrasive and non-fragile materials thathave low densities, such as flour, potato starch, cornstarch, calciumcarbonate, hydrated lime, activated carbon, zinc oxide or other solids.

Dense phase conveying systems are generally characterized by lower inertgas velocities and much higher conveying pressures operating in acontinuous batch mode. Dense phase conveying systems are typically usedto convey abrasive and/or friable material, such as silica sand, flyash, alumina, carbon black, cocoa beans, hazel nuts, corn, plasticpellets, puffed rice, or solids particles that soften at temperaturesgenerated in a convey system. In such systems, a containment vessel isfilled (typically by gravity feed) with the particulate material,sealed, and then pressurized to the desired high pressure. Subsequentrelease of the pressure discharges the material and propels it along theconveying pipe to its intended destination. The stream travel atvelocity typically between 1000 and 3000 ft/min, and the conveyingpressure may be as high as 60 psig. In contrast to dilute phaseconveying systems, dense phase conveying systems utilize higher ratiosof particulate material to the amount of gas used and thus have highersolids loading. In a dilute phase system the stream velocities are to bemaintained at a level to ensure the particles are suspended in the gasand moved through the piping.

SUMMARY OF THE INVENTION

Disclosed herein is a method of conveying solid particles in a pipingcircuit that includes flowing a mixture of the solid particles and a gasin a first portion of the piping circuit, and at a velocity at least asgreat as a pick up velocity of the particles, directing the mixture intoa second portion of the piping circuit having a flow area greater than aflow area of the first portion of the piping circuit, and in which avelocity of the mixture is at least as great as a saltation velocity ofthe particles, and directing the mixture through the second portion ofthe piping circuit to a terminal location. In an example the gas is aprocess gas or a mixture of an injection gas and a carrier gas.Alternatively, the carrier gas and the particles are introduced into thefirst portion from a process vessel. In one example the first and secondportions are within a closed system, and an initial point of the firstportion and the terminal location are at a designated pressure. In analternative to this example the flow areas are sized so that dynamicpressure losses in the first and second portions are less than apressure differential between the initial point and the terminallocation. In an embodiment the particles include a solid polymer, andoptionally the gas is hydrocarbon gas.

Also disclosed herein is a piping circuit for conveying particles thatis made up of a first segment having, a junction in communication with asource of particles, a first flow path having a flow of motive gas, theflow path having a cross sectional area strategically sized so that whenthe particles and gas are flowing along the flow path, the particles areat a velocity at least as great as a pick up velocity of the particles.The piping circuit of this example includes a second segment having, asecond flow path having an upstream end in communication with the firstflow path, a terminal end distal from the upstream end, and a crosssectional area greater than the cross sectional area of the first flowpath and strategically sized so that when the motive gas and theparticles flow through the second segment the particles are at avelocity at least as great as a saltation velocity of the particles. Inan example, the gas is a process gas. In an embodiment the junction isin communication with a discharge line from a process vessel, and theprocess vessel is the source of the particles. In an alternative to thisexample the process vessel contains a second gas that flows with theparticles to the junction. Embodiments exist where pressures at thejunction and at the terminal end are fixed, and a flow rate of the gasand particles are fixed, and where the cross sectional areas of thefirst and second segments are sized so that a pressure drop in the firstand second segments is no greater than a difference in pressure betweenfixed pressures. The terminal end is optionally at an elevation greaterthan the junction.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of an example of a gas handlingsystem

FIG. 2 is a schematic representation of an alternate example of the gashandling system of FIG. 1 .

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying drawings inwhich embodiments are shown. The method and system of the presentdisclosure may be in many different forms and should not be construed aslimited to the illustrated embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey its scope to those skilled in the art.Like numbers refer to like elements throughout. In an embodiment, usageof the term “about” includes +/−5% of a cited magnitude. In anembodiment, the term “substantially” includes +/−5% of a citedmagnitude, comparison, or description. In an embodiment, usage of theterm “generally” includes +/−10% of a cited magnitude.

It is to be further understood that the scope of the present disclosureis not limited to the exact details of construction, operation, exactmaterials, or embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. In the drawingsand specification, there have been disclosed illustrative embodimentsand, although specific terms are employed, they are used in a genericand descriptive sense only and not for the purpose of limitation.

Schematically represented in FIG. 1 is an example of a gas handlingsystem 10 where gas from a gas source 12 is routed to a terminallocation 14 and along a flow path FP that extends through a pipingcircuit 16. In this example shown gas source 12 is illustrated as avessel, alternate embodiments include any source of gas, such as a tank,line, well, compressor, and pump. Terminal location 14 is depicted as aclosed vessel; alternatives exist that include an open container, suchas a bin, tray, car, trough, conveyer, or any place where the contentsflowing through piping circuit 16 are discharged. In the illustratedexample piping circuit 16 is tubular and shown made up of segments 18,20 coupled to and in fluid communication with one another. Segment 18 isillustrated as having an upstream end connected to and in communicationwith gas source 12 so that gas selectively flows from gas source 12 intosegment 18. For the purposes of discussion herein, where segment 18connects to gas source 12 is referred to as an initial point of thepiping circuit 16. A downstream end of segment 18 distal from gas source12 couples to an upstream end of segment 20 via a swage 22. In theexample of FIG. 1 , an inner diameter of segment 20 exceeds that ofsegment 18, and a cross sectional area of the flow path FP between gassource 12 and terminal location 14 changes across swage 22. An innerdiameter of an end of the swage 22 that connects to segment 18 issubstantially the same as that of the segment 18. Similarly, theopposite end of the swage 22 shown connected to segment 20 has an innerdiameter substantially the same as segment 20. In the example of FIG. 1, the inner diameter of the swage 22 increases with distance away fromsegment 18 and proximate segment 20.

Optionally, the inner diameter of swage 22 is stepped and changes at adiscrete location along flow path FP. Examples of gas include any gas orvapor; and in specific examples includes one or more of air, oxygen,hydrogen, nitrogen, hydrocarbons, and the like.

Still referring to the example of FIG. 1 , an example of a particlesource 24 is schematically illustrated and that selectively contains anamount of particles P. In an embodiment particles P are substantiallysolid and have a size and density to be flowable within a tubular byaddition of a motive gas. Examples of the particles P within particlesource 24 include catalysts, polymer particles, additives, and the like.Embodiments exist where the particles P have different sizes, and whichvary depending on a particular application. Line 26 of FIG. 1 isdepicted having an inlet end connected to particle source 24 and inwhich the particles P are selectively received, and then conveyedthrough line 26 to an end distal from particle source 24; which asillustrated connects to segment 18 at intersection 27 shown upstream ofswage 22. Particle source 24 is in communication with segment 18 vialine 26. Alternate embodiments exist where the particles P areintroduced at the initial point or downstream of intersection 27. In anon-limiting example of operation particles P are introduced into pipingcircuit 16 via line 26 and carried to terminal location 14 by gasflowing through circuit 16. Further illustrated in FIG. 1 are optionalcontrol valves 28, 30 shown respectively in segment 18 and line 26, andfor controlling the flow of gas and particles through these conveyancesmeans.

In one embodiment, a flow rate of gas from gas source 12 flowing throughsegment 18 is at a velocity at least as great as a designated pickupvelocity so that the particles P from particle source 24 enteringsegment 18 become dispersed within, and flowable along with, the flow ofgas in segment 18, and do not accumulate along a lower surface of thesegment 18. In one example of operation, the particles are distributedwithin the flowing gas in segment 18 and what is referred to as dilutephase conveying. Further optionally, the inner diameter of segment 18 issized so that an anticipated flow of gas combined with the anticipatedrate of particles P within segment 18 make up a stable dilute phase. Asnoted above, the inner diameter of segment 20 is greater than that ofsegment 18, and in the illustrated example a velocity of the gas andparticles P flowing along flow path FP in segment 20 and downstream ofswage 22 is less than that in segment 18. Further in this example, theinner diameter of segment 20 is set at a value so that the particles Pflowing within the gas in segment 20 are at a velocity greater than whatis referred to commonly as a saltation velocity. In one embodiment,saltation velocity is that at which particles inside of a flow of fluiddrop from their suspended state within the flow of fluid and drop to asurface below the flowing fluid. In a non-limiting example, swage 22 islocated a distance L downstream from intersection 27 where particles Pare introduced into flow circuit. In an example, the distance L is setto be at least a distance of travel after introduction into a flowstream upon which the particles P are no longer accelerating or slippingin the flow stream, but traveling at substantially the same velocity asthe carrier gas.

The piping circuit 16 of FIG. 1 with its increase in cross sectionalarea provides an advantage over known piping circuits that do not have achange in cross sectional area. In an embodiment, by strategicallysizing the section where particles P are introduced into piping circuit16 so that the mixture of gas and particles when flowing through thatsection of piping circuit 16 are at a velocity above a pick-up velocityof the particles P, the particles P will not collect or rest within thepiping circuit 16. A further advantage of the piping circuit 16 is thatincreasing its cross sectional area downstream of the section where theparticles P are introduced limits pressure losses in the piping circuit16 so that the flow of the mixture of gas and particles P retainssufficient kinetic energy to reach the terminal location 14 at avelocity above the saltation velocity. A yet additional advantage isrealized by reducing dynamic loads by maintaining stable dilute phaseconveying. Dynamic loads on a transfer system can result in failure ofconvey piping, supports, structure to where the convey piping isattached to the structure for system only designed for static loads. Itis believed it is within the capabilities of one skilled in the art tosize the segments 18, 20 so that the particles P being introduced intothe piping circuit are introduced into a gas at least as great as apickup velocity, and that over the length of the piping circuit 16 thevelocity of the flow of the mixture of particles and gas is at leastthat or greater than a saltation velocity. Further, it is within thecapabilities of one skilled to size lines to match designated pressureprofiles required in the gas handling system 10.

An alternate embodiment of the gas handling system 10A is shownschematically in FIG. 2 . In this example, another segment 32A is shownintroduced within piping circuit 16A. In this example segment 32A has adiameter and thus area less than that of each of segment 18A, 20A. Assuch, the velocity of the gas from gas source 12A and flowing throughpiping circuit 16A and within segment 32A is at least as great as apickup velocity necessary for particles P being introduced from theparticle source 24A. Moreover, in this example, the linear length ofsegment 32A is less than the length of segment 18 of FIG. 1 , so that anoverall loss of pressure in the gas through piping circuit 16A can bereduced over that of FIG. 1 and in piping circuit 16. Swages 22A1, 22A2are shown for providing changes in line sizes between segments 18A and32A, and segment 32A and segment 20A. Further optional embodiments existwhere in lieu of the segment 32A, a localized pipe diameter is reduced,such as through a venturi or other similar local velocity increasingdevice.

Optional embodiments exist where gas is a gas which examples of whichinclude a processed gas, a mixture of injection gas and a carrier gas.In an alternative the carrier gas and particles are introduced intoportion 18, 18A from a process vessel. Examples of processed gasesinclude hydrocarbon gases. A specific example of gas is provided inTable 1 of Example 1 below.

Example

In a non-limiting example of operation, a polypropylene copolymer, withan ethylene content from 3 to 10%, and a particle size of 1.8 mm isconveyed within a flow of gas. Example constituents of the gas flowingin the line include hydrogen, ethylene, ethane, propylene, and propane,and in Table 1 below are values for the mass of the mixture flowingthrough the line in different simulation cases and the conditions withinthe pipe at the pickup end. Reflected in the data provided in Table 2are simulations Case 1 and Case 2; where in Case 1 the pipe diameterfrom pick-up point to a terminal location is unchanged. In Case 2, thematerial flow rate and conditions are the same as in Case 1, but thesize of cross sectional area in the pipe changes downstream of where theparticles are introduced into the pipe. As illustrated in Table 2, thevelocity of material flow at the pick-up point is 17.5 m/s, which is atrisk of being too low a velocity for satisfactorily conveying particlesas it is estimated that a strand phase could develop at a velocity of17.0 m/s. In Case 2, the pipe diameter where the particles areintroduced is less than that of Case 1 and results in a velocity ofmaterial flow to be 24.1 m/s; a magnitude of which is deemed sufficientto avoid development of a strand phase. Also in Case 2, at a locationdownstream of the pick-up point the pipe diameter is increased; whichreduces dynamic losses of the material flowing in the pipe so that thepressure at the end of the pipe is at 1.0 Barg.

TABLE 1 Simulation Simulation Case 1 Case 2 Conveying Mode Dilute PhaseDilute Phase Conveying mass throughput Kg/hr 50000 50000 Conveying PipeI.D. Mm 154.1 128.2/154.1 Conveying Pipe Length M 73.9 12.0/61.9Conveying Pipe Height M 52  4.7/47.3 No. of Bends 4 4 Conveying gasvolumetric flow M3/min 52.3 52.3 Conveying Pressure (at Pick-up) Barg2.21 2.36 Conveying pressure (at end) Barg 1.0 1.0 Gas Velocity (atpick-up) m/s 17.5 24.1 Gas Velocity (at end) m/s 28.0 28.0 Solids-to-gasratio (mass) 16.4 16.4

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. For example, additional gas can be added, but implementation ofthe method and system described minimizes the need for additional gas.These and other similar modifications will readily suggest themselves tothose skilled in the art, and are intended to be encompassed within thespirit of the present invention disclosed herein and the scope of theappended claims.

What is claimed is:
 1. A piping circuit for conveying particlescomprising: a first segment comprising an intersection where particlesdispersed in a first gas combine with a second gas form a mixture, across sectional area inside the first segment strategically sized sothat when the mixture flows through the first segment the particles areat a velocity at least as great as a pick up velocity of the particles,the intersection comprising a junction where a first pipe carrying thefirst gas and the particles joins directly with a second pipe carryingthe second gas so that the first gas and particles are introduceddirectly into a flow of the second gas within the second pipe; and asecond segment comprising an upstream end in communication with thefirst segment, a terminal end distal from the upstream end, and a crosssectional area greater than the cross sectional area of the firstsegment and strategically sized so that when the mixture flows throughthe second segment the particles are at a velocity at least as great asa saltation velocity of the particles.
 2. The piping circuit of claim 1,wherein the second segment is strategically positioned a length L fromthe intersection to limit pressure losses of the mixture and so that themixture retains sufficient kinetic energy to reach the terminal locationat a velocity above the saltation velocity.
 3. The piping circuit ofclaim 1, wherein the intersection is in communication with a dischargeline from a process vessel, and where in the process vessel comprisesthe source of the particles.
 4. The piping circuit of claim 3, whereinthe process vessel comprises a second gas that flows with the particlesto the intersection.
 5. The piping circuit of claim 1, wherein pressuresat the intersection and at the terminal end are fixed, and a flow rateof the gas and particles are fixed, and wherein the cross sectionalareas of the first and second segments are sized so that a pressure dropin the first and second segments is no greater than a difference inpressure between fixed pressures.
 6. The piping circuit of claim 1,wherein the terminal end is at an elevation greater than the junction.7. The piping circuit of claim 1, further comprising a particle source,and wherein the particles are stored within the particle source, andwherein the particles are selectively conveyed from the particle sourceto the first segment through a line that connects between the particlesource and the first segment.
 8. The piping circuit of claim 1, whereinthe second segment is spaced a distance downstream of the intersectionso that the particles P are traveling in the second segment atsubstantially the same velocity as carrier gas in the mixture.